[GSBN] Lightweight concrete roofs

Mon Jun 21 20:45:59 UTC 2010

Hi all

Anyone have any idea what kind of insulation one could expect out of such a
roof?

And how might one attach a ceiling for insulation to such a structure?

I am designing a structure at the moment, which is based on a series of
hyperbolic parabaloids where cost is a major constraint. We are using poles
with a reed ceiling overlaid with Hessian and then a straw paper clay mix
followed by an insulative water resistant breathable plaster. The premixed
top coat product is called "Thermosim". It stuck me that the latex cement
idea could offer a potential alternate cost effective option.

On another note, I have seen a roof over a twin vault compost toilet at an
eco village called Thlolego, where some kind of cement slurry over a Hessian
cover on off-cut boards was used. I am not sure about whether or not latex
was used in the mix, but it's finish was clearly some kind of latex paint.
However I noticed the last time I visited a couple of years ago that the
Hessian had started to rot with a dark mould having developed and a green
kind of algae/moss growing through it. The structure was about 12 years old.
I don't have an understanding of the effect of latex on cement but in the
long run I am wondering if natural fabrics are such a good idea with cement
for roofs - due to differences in the PH and the moisture contents of such
materials. 

Any one have an  idea of what kind of idea moisture content or what PH a
latex cement would have?

I also wonder what the effects of varying levels of humidity would have on
such structures? The Thlolelgo project is even situated in a pretty dry part
of the world.

I would think a geofabric (we call it Bidim) would also make a good and cost
effective alternative to fibreglass. There is also a product that I use for
building sand bag structures, called "Spunbond" which is a woven polyester
and is even more cost effective, which would probably be even better. We get
it locally made here, but I know that one supplier get's their supply from
Germany. While not UV stable the fabric does not degrade in the presence of
high alkalinity products like cement. 

On this note however, any idea how thick a coating of latex cement would one
need over the fabric to protect it from UV degradation?

How old are the examples of these latex cement roofs?

Thanks 

Andy Horn

-----Original Message-----
From: GSBN-bounces at greenbuilder.com [mailto:GSBN-bounces at greenbuilder.com]
On Behalf Of Jim Carfrae
Sent: 21 June 2010 06:29 PM
To: (private, with public archives) Global Straw Building Network
Subject: Re: [GSBN] Lightweight concrete roofs

This is an aside on the topic of lightweight concrete roofs - My
grandfather, Jim Waller, was a civil engineer and innovator in the use of
concrete (he built the first concrete boats for the admiralty during the 2nd
world war). The reason why I mention him is that in the 1950s he developed a
building system that has similarities with the Nez roof. His system was
called Ctesiphon after the ancient arch in Iraq, and basically involved
building a temporary structure based on a series of inverted catenary arches
as ribs and covering them with an envelope of Hessian fixed to the ribs. The
hessian was covered with thin coats of a cement slurry (no latex in his day)
This was designed to sag between the ribs causing corrugations which gave
the shell its structural integrity. The trick was that the arched forms
could now be removed and reused, leaving a self supporting lightweight
concrete shell.

The system was used for grain silos in Egypt, emergency housing in India and
a whiskey storage shed in Ireland among other projects, but never took off
in a big way and has remained an interesting byway. As soon as I followed
the link to the Nez roof I was reminded of my grandfathers work - it seems
they would have had a lot in common.

Thanks

Jim

Jim Carfrae

PhD Research Student

Room 119, Reynolds Building

University of Plymouth

Drake Circus

Plymouth

PL4 8AA

jim.carfrae at plymouth.ac.uk

07880 551922

01803 862369

________________________________________

From: GSBN-bounces at greenbuilder.com [GSBN-bounces at greenbuilder.com] On
Behalf Of Paul Olivier [paul.olivier at esrint.com]

Sent: 21 June 2010 16:51

To: (private, with public archives) Global Straw Building Network

Subject: Re: [GSBN] Lightweight concrete roofs

Mark,

Please forgive me for asking dumb questions about something you have
written:

It sounds as though there is plenty of resources for the mix so I won't
address that too much now...it's not rocket science. You basically use the
latex as you would water for a cement mix with sand. You can use as little
latex mixed with water as seems effective...more latex (50/50) to water for
the initial coat. I can attest that the system works well and can be low
cost. It is easy to learn and quick to build.

I am keenly interested in use of latex with cement,

and I would like to find a good summary of the steps involved.

We will soon start building outhouses in a ferro-cement over urine-diverting
toilets,

and it is critical that moisture does not penetrate the structure over time.

This effort is summarized at: http://www.esrla.com/pdf/toilet.pdf

Today we are putting up the first ferro-cement structure as depicted in this
presentation.

We must get it right, and your advice would be greatly appreciated.

Thanks.

Paul

On Mon, Jun 21, 2010 at 9:47 PM, MARK SCHUENEMAN
<huffnpuff at q.com<mailto:huffnpuff at q.com>> wrote:

Greetings All interested parties,

The 'Nez' Roof system has certainly progressed beyond the experimental
stages. The are many roofs around the world thanks to George and Al Knott.
The reason George didn't return your email is probably he just returned from
training folks his roof system in Uganda where they did a roof for a
performing arts center. I know there's Nez roofs in Afghanistan, Kenya,
Rwanda as well as many other working demo structures in the Denver area and
the mid west US. He has trained his roof system to many folks , including
myself, and we've built the system many times around the world. His model of
'roof first' makes sense. He was working with a minister in Afghanistan
after their earthquake when all they had was tarps. Snows would collapse the
tarps when they could have built his roof with mostly salvaged materials and
used the tarps and more salvaged materials for walls. Recently he's been in
conversations with some folks in Haiti, so he could get you in touch with
them.

George is a wonderful man with a vision and plan and energy abundant for a
Ninety year young fellow. Mr. Nez started doing disaster relief work for the
federal Government in Central America years ago. He has always been more
than happy to share his knowledge with anyone interested. As a matter of
fact, you may want to make a pot of tea for a conversation with George. He
is a most knowledgeable resource when it comes to disaster relief. If you
have a project going somewhere I'd guess George is a suitcase packing away
from joining you for a demo of his roof system, as would I, or to discus
your project.

His system is more about the shape of the structure and the latex coating
but the 'fabric' for the roof has been an evolution. He used to weave a
fiberglass netting for the latex parging but has worked with and tested
regular old cotton fabric (or even tarps) with chicken mesh. These materials
seem more readily available in most parts of the world and cheaper. The
frames can be made of salvaged materials and spliced effectively. The latex
for the concrete parging can be old left over (or oops) paints, if you can
live with the color. It sounds as though there is plenty of resources for
the mix so I won't address that too much now...it's not rocket science. You
basically use the latex as you would water for a cement mix with sand. You
can use as little latex mixed with water as seems effective...more latex
(50/50) to water for the initial coat. I can attest that the system works
well and can be low cost. It is easy to learn and quick to build.

The latex parging seems very durable, flexible (elastic), waterproof and
enduring. The material itself is not that difficult to work with other than
that it doesn't lend itself to a great esthetic. My guess is that if you're
homeless, cold or hot and wet, you could care less about esthetics. Once you
apply the parging with a few strokes of a brush or trowel further strokings
only drag, ball and/or tear. I got some on my vehicle and missed cleaning it
until the next day and when I removed it some paint came with it...it's
sticky. Clean your tools soon and often.

If interested please feel free to write myself or George
geonez at peoplepc.com<mailto:geonez at peoplepc.com> or call me with your
thoughts or inquires.

Regards,

Mark Schueneman

303-444-6027 hm.

303-591-9841 cell

> From: bob at bobtheis.net<mailto:bob at bobtheis.net>

> Date: Sat, 19 Jun 2010 22:57:55 -0700

> To: GSBN at greenbuilder.com<mailto:GSBN at greenbuilder.com>

> Subject: Re: [GSBN] Lightweight concrete roofs

> 

> We've been considering this technique for work in Haiti, but I never

> got a reply to my email to George Nez, asking, among other things,

> whether the technique has progressed beyond the experimental roof at

> the University of Colorado.

> 

> Does anyone know of further work with it? I'm especially wondering if

> someone has tried making corrugated or folded plate panels.

> 

> Bob Theis

> 

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> GSBN at greenbuilder.com<mailto:GSBN at greenbuilder.com>

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--

Paul A. Olivier PhD

27C Pham Hong Thai Street

Dalat

Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)

Mobile: 063 399 7256 (in Vietnam)

Skype address: Xpolivier

http://www.esrla.com/

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